Position Effects in Web Search Click Behavior

When a search engine presents a set of document links, the rates and characteristics of clicks on each link may be influ-enced by display effects. Users may be more predisposed to click on some positions than others, whether due to atten-tion and reading order, their interpretation of the position as additional relevance information, or other reasons. We quantify this effect, and fit models for the influence of these position effects on clickthrough. We also fit empirical prior distributions to clickthrough rates, and use posterior esti-mation as a smoother of empirical averages